Bring iwn_update_htprot() back, so iwn(4) will properly keep track

Bring iwn_update_htprot() back, so iwn(4) will properly keep track
of HT protection changes while associated.

HT protection affects behaviour on Tx but is configured along with Rx settings
(because Intel likes it that way). And our previous iwn_update_htprot()
implementation had a bug where it would accidentally clear bits which enable
CCK rates for Rx. The Intel Wireless-N 2200 chip accordingly stopped receiving
some frames (most notably broadcast frames) and the link broke down.

Also, restore the power-saving level after updating the Rx config (like
Linux does), and add some DELAYs for good measure to ensure the firmware
has time to process asynchronous commands we send.

tested by myself and mlarkin@
ok mlarkin@